7 Answers
7

I don't think there's an ideal or not ideal. It can be a good technique for accuracy, but you lose speed. It is worthwhile having as another technique in your arsenal.

I use it a lot and I think practice will make it less of a strain for you, but you will also find that you can improve your free hand accuracy over time anyway so you'll probably end up only using it for specific runs or sections..

I had a teacher who told me to do this and at the time it was great. I wasn't getting into very advanced playing so I didn't need that extra mobility.

There's nothing wrong with doing it, but you won't always want to because it does limit your mobility in you picking hand. Also, if it's causing any pain, you really shouldn't do it. It won't go away, and it could cause long term injury. You should either find a different way of anchoring your pinky or stop doing it altogether.

It's a matter of some contention... There are those who maintain you shouldn't and others who do it all the time.
I do so if I'm "Travis picking", seems to help with accuracy. However, not when I'm playing jazzy complex chords as I use more fingers...
And never when flatpicking.

Maybe you should, maybe you shouldn't. The fact is that a lot of guitar players do this (John Frusciante comes to mind):

I personally tried to do this but didn't find it helpful. If some day you find yourself really uncomfortable doing it, you'll just stop. In fact, people tend to overstate the power of habit: it's not like it will take you years to stop doing it. While it helps you, stick with it.

When I first started to learn the default seemed to be to place the little finger to anchor. As I progressed I found that naturally I was actually doing it less and less. What I would say was that it did help in the beginning as it encourages your muscle memory for where the strings are, I think that is the logic behind it.

Actually this is not a very good technique.
You are not supposed to rest your finger. If you watch famous guitarist, you 'll probably see that they follow this technique, but they only use it while performing, and, I guess, without noticing it.
For example, Jimi Hendrix, Eric Clapton, John Frusciante, etc.

But of course you know you are not Jimi Hendrix, and even these players, I believe try to avoid resting the little finger while they practice.

If you want to check what's the best technique, you should definitely see videos of great Jazz player, who usually have an excellent technique even while performing.